Stonehenge

Built between 3000 and 2000 BCE, Stonehenge is a monument of some kind made from giant foreign rocks that were moved somehow. Given that it highlights astronomical events like solstices and eclipses, it was presumably for worshipping or measuring...something. That's pretty much what we know. But the monument's silent beauty is only enhanced by the mystery of its construction and function in the lives of the people who made it all those millennia ago.